1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly to a method of inspecting a semiconductor workpiece for carbon-based films using Raman spectroscopy.
2. Description of the Related Art
Accurate and reliable defect inspection is vital to successful semiconductor fabrication. Microelectronic circuit structures may be highly sensitive to contamination by particulates introduced by various semiconductor processing tools and to the various deleterious effects associated with unwanted residual films left over after semiconductor processing steps. Most semiconductor chip fabrication techniques involve the sequential application of films of various compositions on a silicon wafer or substrate. The successful application of the stacked films often requires a relatively pristine underlying surface upon which each successive layer is formed. However, the presence of an unwanted residual film on the underlying layer may cause the overlying film to later delaminate and lead to device failure. Examples of unwanted residual films remaining after a given semiconductor processing step are legion. One example involves the formation of residual graphitic carbon following carbon-based photoresist stripping. Carbon-based photoresists are commonly used as masking materials for etching, ion implantation and various other semiconductor processing steps.
A given process for fabricating an integrated circuit may entail scores of different photomask steps, each involving the application and removal of a resist film. In many modern semiconductor fabrication processes, mask removal involves a plasma based removal or ashing step that is followed by some type of aqueous acidic or solvent cleaning process, such as a so-called RCA solvent cleaning. The plasma process converts some of the carbon present in the photoresist into graphitic-form carbon. Whether in graphite form or not, the resist strip process may not completely remove the carbon based resist material and thus leave a graphitic carbon residue on the wafer. It is highly desirable to be able to detect the presence of a carbon based residue film following resist strip and to be able to discriminate between graphitic form carbon and non-graphitic-form carbon. The presence of graphitic-form carbon indicates a possible shortcoming in the ashing and/or the solvent resist stripping process. Non-graphitic carbon may be present in the form of various hydrocarbon complexes and may be indicative of contamination from processing chamber walls or plumbing or from residual compounds left over from anisotropic etching processes utilizing fluorocarbons.
Various techniques have been used as a means of detecting the presence of carbon-based residual films on semiconductor wafers. Scanning electron microscopy (xe2x80x9cSEMxe2x80x9d) has been used as a means of identifying the presence of thin films in general, and attempts have been made to apply it to the identification of carbon based residues. Many SEM instruments are provided with an electron disperse x-ray spectrometer (xe2x80x9cEDXxe2x80x9d) that can identify the elemental composition of a contaminant film. However, SEM does not necessarily provide an exact identification of the chemical composition of the material inspected. For example, SEM with EDX generally cannot distinguish allotropic species. Furthermore, a time-consuming vacuum pump-down is required prior to the performance of the SEM scan.
Time of flight secondary ion beam spectroscopy (xe2x80x9cTOF SIMSxe2x80x9d) has also been used as a method of inspecting for carbon based residues. However, TOF SIMS is destructive of the scanned structure, and like SEM, requires vacuum conditions and the associated pump down times.
The present invention is directed to overcoming or reducing the effects of one or more of the foregoing disadvantages.
In accordance with one aspect of the present invention, a method of inspecting a workpiece for carbon residue is provided. The method includes directing coherent radiation at the workpiece to produce Rayleigh scattered radiation and Raman scattered radiation. The Rayleigh scattered radiation is filtered out. A spectrum for the Raman scattered radiation is detected and compared with a known Raman spectrum for carbon.
In accordance with another aspect of the present invention, a method of inspecting a semiconductor wafer for carbon-based photoresist residue is provided. The method includes directing coherent radiation at the wafer to produce Rayleigh scattered radiation and Raman scattered radiation. The Rayleigh scattered radiation is filtered out. A spectrum for the Raman scattered radiation is detected and compared with a known Raman spectrum for graphitic carbon.
In accordance with another aspect of the present invention, a method of processing a semiconductor workpiece that has a carbon-based resist film is provided. The method includes stripping the carbon-based resist film and inspecting the workpiece for carbon-based residue by directing coherent radiation at the workpiece to produce Rayleigh scattered radiation and Raman scattered radiation. The Rayleigh scattered radiation is filtered out and a spectrum for the Raman scattered radiation is detected and compared with a known Raman spectrum for carbon.